20

Beetle life cycle

BEETLE LIFE CYCLE

mobility. Some are blind, others legless, and beetle

larvae consume a wide range of substances, but

many live surrounded by food and do nothing

except eat and grow. As they grow they molt,

casting off their old cuticle and inflating the new,

soft one beneath with air to give them space to

grow until the next molt, a process called

“ecdysis.” After a number of molts, the fully

grown larva searches for a place to pupate. The

pupa is a quiescent stage, hardly able to move,

so unable to escape from predators, parasites,

dehydration, or flooding, making pupation a

vulnerable period in the insect’s development.

Many beetles pupate deep inside substrate,

making a protected pupal cell in the soil or in

dead wood. Inside the pupa, the internal organs

Beetles are holometabolous insects, which means

that they have complete metamorphosis, an

extraordinarily complex but successful adaptation

that has probably only evolved once in the history

of life. Other such insects include the other three

hyperdiverse insect orders, Diptera (true flies),

Hymenoptera (bees, ants, and wasps) and

Lepidoptera (butterflies and moths). These four

orders combined total over 820,000 named

species, so together they account for considerably

more than half of all known animal life,

suggesting that complete metamorphosis is

correlated with astonishing diversity.

So, what is complete metamorphosis? Most

people are familiar with the life cycle of a butterfly,

and the basic life cycle of a beetle or any other

holometabolous insect is essentially the same. The

female lays fertilized eggs, which hatch into larvae

(also called, depending on the group, grubs,

maggots, or caterpillars). These are a feeding

stage and have limited sense organs and limited

below left | Hypera rumicis

(Curculionidae) The latticed

pupal cases of this externally

feeding weevil in England, UK,

give some protection from

predators and parasitoids.

below right | Omaspides

(Chrysomelidae: Cassidinae)

A tortoise beetle from Ecuador

shows parental care of a brood

of more than 30 larvae. Larvae

retain their excrement, as a

physical and chemical defense.